AT29C040A-12JC Просмотр технического описания (PDF) - Atmel Corporation

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AT29C040A-12JC

4-megabit (512K x 8) 5-volt Only 256-byte Sector Flash Memory

Atmel Corporation 

be performed. The software protection feature may be enabled or disabled by the user; when

shipped from Atmel, the software data protection feature is disabled. To enable the software

data protection, a series of three program commands to specific addresses with specific data

must be performed. After the software data protection is enabled the same three program com-

mands must begin each program cycle in order for the programs to occur. All software program

commands must obey the sector program timing specifications. The SDP feature protects all

sectors, not just a single sector. Once set, the software data protection feature remains active

unless its disable command is issued. Power transitions will not reset the software data protec-

tion feature, however the software feature will guard against inadvertent program cycles during

power transitions.

After setting SDP, any attempt to write to the device without the three-byte command sequence

will start the internal write timers. No data will be written to the device; however, for the duration

of tWC, a read operation will effectively be a polling operation.

After the software data protection’s 3-byte command code is given, a byte load is performed by

applying a low pulse on the WE or CE input with CE or WE low (respectively) and OE high. The

address is latched on the falling edge of CE or WE, whichever occurs last. The data is latched by

the first rising edge of CE or WE. The 256 bytes of data must be loaded into each sector by the

same procedure as outlined in the program section under device operation.

4.5 Hardware Data Protection

Hardware features protect against inadvertent programs to the AT29C040A in the following

ways: (a) VCC sense – if VCC is below 3.8V (typical), the program function is inhibited; (b) VCC

power on delay – once VCC has reached the VCC sense level, the device will automatically time

out 5 ms (typical) before programming; (c) Program inhibit – holding any one of OE low, CE high

or WE high inhibits program cycles; and (d) Noise filter – pulses of less than 15 ns (typical) on

the WE or CE inputs will not initiate a program cycle.

4.6 Product Identification

The product identification mode identifies the device and manufacturer as Atmel. It may be

accessed by hardware or software operation. The hardware operation mode can be used by an

external programmer to identify the correct programming algorithm for the Atmel product. In

addition, users may wish to use the software product identification mode to identify the part

(i.e. using the device code), and have the system software use the appropriate sector size for

program operations. In this manner, the user can have a common board design for 256K to

4-megabit densities and, with each density’s sector size in a memory map, have the system soft-

ware apply the appropriate sector size.

For details, see Operating Modes (for hardware operation) or Software Product Identification.

The manufacturer and device code is the same for both modes.

4.7 DATA Polling

The AT29C040A features DATA polling to indicate the end of a program cycle. During a pro-

gram cycle an attempted read of the last byte loaded will result in the complement of the loaded

data on I/O7. Once the program cycle has been completed, true data is valid on all outputs and

the next cycle may begin. DATA polling may begin at any time during the program cycle.

4.8 Toggle Bit

In addition to DATA polling the AT29C040A provides another method for determining the end of

a program or erase cycle. During a program or erase operation, successive attempts to read

4 AT29C040A

0333K–FLASH–2/05

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